A fuel cell system such as a household cogeneration system includes a fuel processing apparatus that generates hydrogen-containing gas and a fuel cell that generates electricity using the hydrogen-containing gas generated by the fuel processing apparatus (for example, see PTL1 and 2).
As illustrated in FIG. 9, fuel processing apparatus 100 for a conventional fuel cell system includes: combustion section 102 including burner 23; desulfurization section 105 provided to surround combustion section 102, which removes sulfur component from a source gas such as hydrogen carbonate fuel including city gas, LPG, and others; vaporization flow channel 108 in which the source gas and steam are mixed; reforming section 103 that causes a steam reforming reaction of mixed gas at a high temperature of approximately 600° C. and generates hydrogen-containing gas having hydrogen as the main component, conversion section 106 in which the concentration of carbon monoxide which is poisonous to the catalyst of a fuel cell is reduced to approximately 0.5% by the CO shift reaction, and selective oxidation section 110 that further reduces the carbon oxide concentration to approximately 10 ppm or lower by the selective oxidation reaction (for example, see PTL 3).
It is preferable that the temperature of desulfurization section 105 is set and maintained to a high temperature of 250° C. to 300° C., which is an optimum temperature for a hydrodesulfurization catalyst. In addition, it is preferable that the source gas provided to desulfurization section 105 is heated to an optimum temperature for the catalyst so as to promote the hydrodesulfurization reaction. Preheating, by the heat of the combustion section, before source fuel is supplied to the desulfurization section has been suggested (see PTL4 and PTL5).
However, as illustrated in FIG. 9, desulfurization section 105 is provided outside of fuel processing apparatus 100. Accordingly, desulfurization section 105 is easily affected by an external environment, making it difficult to set and maintain the temperature of the desulfurization section 105 at an optimum temperature. When the desulfurization section 105 is kept operating at a temperature lower than the optimum temperature, activity in hydrodesulfurization catalyst is reduced, shortening the lifetime of the hydrodesulfurization catalyst. Since the lifetime of a fuel processing apparatus is generally considered as 10 years, there has been a request for a method for reducing the influence of the temperature from external environment.
Furthermore, since a source gas at room temperature is provided to desulfurization section 105, there is a problem that the temperature of the source gas is not raised up to a temperature sufficient for hydrodesulfurization reaction.
As a means for reducing the influence of the temperature of the external environment, providing a heat insulating section at an outer periphery of fuel processing apparatus 100 (desulfurization section 105) has been considered. For example, placing the desulfurization section in a heat insulating section provided around the combustion section has been suggested (see PTL6). However, there is a problem that providing further heat insulation material to the outer periphery of fuel processing apparatus 100 increases the volume of the entire fuel cell system.
Alternatively, the amount of hydrodesulfurization catalyst added to desulfurization section 105 may be increased. However, there is a problem that the increased amount of the hydrodesulfurization catalyst added increases the size of the apparatus and the cost for the fuel processing apparatus. Furthermore, PTL7 discloses, for example, a reforming apparatus in which a vaporization section is provided to surround the reforming section. Although the invention disclosed in PTL7 can reduce the amount of heat emitted from the reforming section, an effect that the influence of the temperature on the desulfurization section from the external environment is reduced is not suggested.
A fuel processing apparatus housed inside an outer package, with a plurality of reactors closely arranged in parallel has been disclosed in PTL8 as a means for keeping the temperature of the source gas at a high temperature. According to the invention disclosed in PTL8, the reformed gas can be used for preheating the source gas. However, according to the configuration, the influence of the temperature of the external environment is reduced by a granular heat insulating material filling the outer package. Accordingly, it is difficult to miniaturize the size of the apparatus. PTL8 does not suggest that the influence of the temperature on the desulfurization section from the external environment is reduced. Accordingly, a fuel processing apparatus not easily affected by the temperature of the external environment has been needed.
Furthermore, as illustrated in FIG. 9, in a conventional fuel processing apparatus, there was a region A where no component is arranged around reforming section 103 that reaches a high temperature. Since reforming section 103 is exposed, it was necessary to provide a thick insulating material at an outer periphery of the apparatus in order to prevent the emission of heat to outside of the apparatus. The more the amount of heat insulating material, the more the volume of the apparatus becomes, despite the need for miniaturization of the apparatus. Furthermore, as illustrated in FIG. 9, conventional conversion section 106 is provided at one part. Since conversion section 106 is cooled on the inner-rim side contacting vaporization flow channel 108, exothermic reaction is mainly occurred on the upstream side of the gas. Accordingly, there is a problem that the reaction efficiency of the converter catalyst is reduced due to uneven temperature distribution in the converter catalyst. In response to the problem, a fuel processing apparatus having a catalyst with high reaction efficiency has been needed.